Production of stretch plastic film

Abstract

Stretch plastic film is formed by extruding suitable plastic material from an annular die as a tubular film, forming the extruded film into a bubble with air entrapped therein by collapsing the tubular film at a predetermined distance from the annular die, causing the temperature of the tubular film when collapsed to be sufficiently high to cause opposite sides of the collapsed film to become bonded together to form a blocked two layer film, and stretching the blocked two layer film to reduce its thickness.

What is claimed is:  
     
       1. A method of producing stretch plastic film including: 
       extruding suitable plastic material from an annular die as a tubular film,  
       forming extruded film into a bubble with air entrapped therein by collapsing the tubular film bubble at a predetermined distance from the annular die,  
       causing the temperature of the tubular film when collapsed to be sufficiently high to cause opposite sides of the collapsed film to become bonded together and form a blocked two layer film, and  
       stretching the blocked two layer film to reduce its thickness.  
     
     
       2. A method according to  claim 1  wherein said stretching is effected by passing the blocked two layer film between a pair of driven stretch rolls rotated at a faster peripheral speed than the speed of the blocked two layer film at said predetermined distance from the annular die. 
     
     
       3. A method according to  claim 2  wherein the blocked two layer film is passed successively through a plurality of pairs of driven stretch/nip rolls, each subsequent pair of stretch rolls being driven at a faster peripheral speed than the previous pair of stretch/nip rolls. 
     
     
       4. A method according to  claim 1  wherein the blocked two layer film is stretched by an amount in the range of from about 100 to about 400%. 
     
     
       5. A method according to  claim 1  wherein the blocked two layer film has a thickness in the range of from about 20 to about 50 microns and is stretched to a thickness in the range of from about 10 to about 25 microns.